20940781 has 2 divisors, whose sum is σ = 20940782. Its totient is φ = 20940780.

The previous prime is 20940763. The next prime is 20940797. The reversal of 20940781 is 18704902.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18412681 + 2528100 = 4291^2 + 1590^2 .

It is a cyclic number.

It is not a de Polignac number, because 20940781 - 2⁵ = 20940749 is a prime.

It is a super-2 number, since 2×20940781² = 877032617779922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20940701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10470390 + 10470391.

It is an arithmetic number, because the mean of its divisors is an integer number (10470391).

Almost surely, 2^20940781 is an apocalyptic number.

It is an amenable number.

20940781 is a deficient number, since it is larger than the sum of its proper divisors (1).

20940781 is an equidigital number, since it uses as much as digits as its factorization.

20940781 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4032, while the sum is 31.

The square root of 20940781 is about 4576.1098107454. The cubic root of 20940781 is about 275.6328389918.

The spelling of 20940781 in words is "twenty million, nine hundred forty thousand, seven hundred eighty-one".